In this Aug. 16 photo, President Barack Obama gestures while speaking in Milwaukee. Some of the 1 in 5 Americans who believe that President Obama is a Muslim are adamant in their convictions, and continue refuting the notion – and evidence – that Obama is a practicing Christian.

Washington — Why is it so hard to convince people that President Obama is not Muslim?

After all, this misperception first surfaced years ago, in the presidential campaign. As far back as 2008, 13 percent of Americans believed Mr. Obama followed the Islamic faith, according to the Pew Research Center.

Now that he’s in the White House, with his every move covered in detail by a ravenous horde of media, you would think that more people would be aware he is a practicing Christian, but that doesn’t appear to be the case. Last week, another Pew poll found that today 18 percent of Americans think their chief executive is Muslim.

Well, many do. Fully 60 percent of those who are convinced Obama is Muslim say they learned that from the media. Thus, one simple answer as to why this mistaken idea persists may be that many of those who hold it sincerely believe it to be the case. They are not uninformed, but misinformed.

This can be seen in a number of e-mailed responses to earlier stories in the Monitor on the Obama/Muslim question that reflect not so much anger as bewilderment that more people don’t know the real facts.

“I don’t understand why you emphasize over and over that some Americans ‘incorrectly’ think Obama is Muslim,” reads one response. “He has said so himself, he has worshipped with Muslims with his shoes off, he has bowed to Muslim leaders and he doesn’t attend a Christian church.”

Another reads: “There is quite a huge chunk of the population that is exasperated by what they see as Obama bending over backwards (if not forward) in deference to Muslim sensibilities. From his first interview on Arab TV, to the bowing to the Saudi king . . . to the Cairo speech, the list goes on and on.”

For the record, Obama’s father was Muslim. As a young child, Obama attended both Muslim and Christian schools in Indonesia, before his mother sent him back to the states to live with his maternal grandparents.

“Barack Obama has an unusual and interesting background . . . however, no evidence supports a claim that Obama is a Muslim (radical or otherwise),” concludes the rumor-debunking website Snopes.com.

Another reason why a large slice of Americans continue to believe that Obama is Muslim may be more general: it appears that factual misperceptions about politics can be surprisingly persistent, even in the face of corrective information.

Those who were then shown corrections to the mock news often were not swayed by the update. They had more faith in the original, misleading piece, particularly if it conformed to their ideological preconceptions.

Messrs. Nyhan and Reifler even documented something of a backfire effect: corrections made some participants cling even more tightly to their mistaken beliefs.

“Corrective information in news reports may fail to reduce misperceptions and can sometimes increase them for the ideological group most likely to hold those misperceptions,” concluded the pair.